This invention relates to an apparatus for detecting, at one end of a communication line, malfunctions of an interface circuit provided on the other end of the communication line. More particularly, this invention relates to an apparatus for detecting a malfunction of an interface circuit of an electronic controller for operating an engine of a vehicle in association with an electronic controller for controlling the transmission.
There have been made attempts to improve shifting performance of electronically controlled automatic transmissions in terms of smoothness and the like. To attain such an improvement, a type of control system is generally adopted in which a signal is supplied from a T/M (transmission) controller to an E/G (engine) controller, and the E/G controller reduces the engine torque on the basis of this signal while the T/M controller reduces the line pressure.
The construction of an example of this conventional control system will be described below in detail with reference to FIG. 1.
As schematically shown in FIG. 1, a CPU 2 of a T/M controller 1 outputs a signal via a communication circuit 3 in order to reduce a shift shock when the speed of the automatic transmission is changed, this signal is input into a CPU (central processing unit) 6 provided in an E/G controller 5 through an interface circuit 7 of the E/G controller 5, and an engine torque reduction signal S.sub.2 is supplied from an output stage 8 of the E/G controller 5 to the engine 11. At the same time, the T/M controller 1 supplies a line pressure reduction signal S.sub.1 to the transmission 10 via an output stage 4 in order to reduce the line pressure, thereby enabling a reduction in the shift shock by the cooperation of the E/G system and the T/M system, thus performing shift control.
However, a further improvement in the control of the cooperation of T/M and E/G systems is expected in order to maintain comfortableness for the occupant during running of the vehicle even in the event that the interface circuit 7 of the E/G controller 5 malfunctions due to, for example, a short circuit or disconnection of a pull-up resistor in the interface circuit caused by vibrations or the like during running (although wiring design and maintenance of the controller have been fully considered in order to avoid such a malfunction).